Learn English – the difference between ‘prepare for the party’ and ‘prepare the party’

They are both nouns and both mean a lack of discipline. However, the word undiscipline is far less common than indiscipline. The latter can be found in most dictionaries, while most dictionaries will not contain undiscipline.

Far more common is the use of undisciplined as an adjective. Though even in this context it would probably be more idiomatic to use a negation of the word disciplined instead, compare:

• He is rather undisciplined.
• He is not very disciplined.

Firstly, both sentences are a subjective opinion given by someone, and they have exactly the same meaning. However, the difference lies in the syntax.

She seems crazy

is considered a personal sentence. This means that it is the opinion of the speaker, and the speaker doesn't shy aware from admitting it.

However,

It seems like she is crazy

is an impersonal sentence (See here for more details and examples). This means that, although it is still the speaker's opinion, they are distancing themselves from it, by saying "It seems that" + their opinion. They are trying to make themselves sound more objective or neutral, even when giving an opinion, which is always subjective.